384 University of California Publications in Zoology [VOL. 11 



Depredations probably increase also as the natural food sup- 

 ply of birds is destroyed and they have to rely on the products 

 of civilization. The change of food caused by change in environ- 

 ment sometimes causes an increase in the number of birds of a 

 species, and thus increases the extent of the depredations. Ap- 

 parently there are a number of birds in California which have 

 directly profited by the change of environment and are increasing 

 in numbers. The linnet, western meadowlark, and mockingbird 

 undoubtedly belong to this class. 



As the crops change, and consequently the food supply, we 

 may even expect that in the future the food habits of birds will 

 change. Hence a knowledge of the food habits of birds at the 

 present time may be of far greater value in the future, when 

 such data are needed for comparison. 



Whether it is best to destroy certain birds because of their 

 depredations, or to preserve them because of their value as insect 

 or weed-seed destroyers, has become a real problem. There is 

 not a farmer who is not at some time of the year confronted 

 with this problem. In a newly settled country the question as 

 to the value of certain birds is often of grave importance. If 

 nature were not so closely woven together we might easily solve 

 the problem by simply exterminating those birds which cause 

 damage. In the early days this was tried. It is experience that 

 has taught us the danger attendant on the indiscriminate ex- 

 termination of any form of life. 



The problem stated, the next thing to be considered is : How 

 shall it be solved? Observation has proved an unsafe method of 

 determining the true value of a bird. Mere sentiment fails to 

 convince a large number of the class of people deeply interested 

 from actual contact with the problem. The method which has 

 proved the most dependable is a thorough scientific investigation. 

 The problem is complex. It involves a knowledge of the life- 

 history of birds, insects, and plants, a conception of the inter- 

 action of organisms, and an appreciation of the accompanying 

 ecological relations. 



A scientific investigation as a means of determining the status 

 of a bird presents just as great possibilities as this method has 

 in other fields. In preventive medicine we see the results of 



